The present work reveals the binding interactions of a credible cancer cell photosensitizer, harmane (HM), with some selected bile salt aggregates of dissimilar hydrophobicity viz. sodium deoxycholate (NaDC), sodium cholate (NaC) and sodium taurocholate (NaTC). The explicit variation of the prototropic equilibrium of the photosensitizer both in the ground and excited state has been utilized to scrutinize the interaction phenomena. Differential modulation in the prototropic equilibrium of HM in the aforesaid aggregates has been explained on the basis of the structural dissimilarities of the bile salt monomers. The contrived hydrophobic surroundings provided by the aggregates have been reflected on the spectroscopic results, especially in the time-resolved fluorescence and the rotational dynamical behavior of the molecule of interest. Slow solvent reorientation time with regard to the lifetime of HM proliferated by the red-edge effect in two specific bile salts namely NaC and NaTC, whereas its absence in NaDC aggregates has also been elucidated on the basis of accessibility of the solvent molecules within the aggregates. © 2017 The American Society of Photobiology

NIKHIL GUCHHAIT

Chemistry

R SETT

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

&nbsp;

The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

&nbsp;

It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Photochemistry and Photobiology

The present study reports a meticulous characterization of the interaction of a potent anti-cancer drug, berberine chloride (BR) with a series of bile salt aggregates having varying hydrophobicity (sodium deoxycholate (NaDC), sodium cholate (NaC), and sodium taurocholate (NaTC)). The absorption spectrum of BR reveals a complex profile comprised of four distinct peaks. Analysis of the modulations of the absorption spectral properties of BR following interaction with the bile salts raising deeper questions unveils a critical insight into the mode of interaction of the cationic drug (BR) with the bile salts; a greater degree of perturbation of the microenvironment of the isoquinolinic part of BR compared to the benzenoid part. The remarkable modulation of the fluorescence profile of BR with added bile salts provides a sensitive indicator for monitoring the interaction scenario. However, an intriguing observation in this context reveals differential fluorescence behavior of BR in various bile salt aggregates, that is, similar observations in NaDC and NaC (which are legitimately interpreted according to the ‘two-step association model’) in comparison to NaTC. Such contrasting behavior of BR in NaTC aggregates has been rationalized on the basis of the possibility of formation of dye aggregate facilitated because of the proximity of the cationic drug molecules to the anionic headgroup of NaTC bile salt. Surprisingly, our spectroscopic results evidence for binding location of the drug at the interfacial region in all the bile salt aggregates. To this end, the time-resolved fluorescence decay behavior of the drug within various bile salt aggregates has been meticulously studied. The fluorescence decay results are found to be highly sensitive to the structure and size of the bile salt aggregates eventually leading to characterization of the interaction of the drug with the bile salts in excellent corroboration with the steady-state data. Furthermore, the time-resolved fluorescence anisotropy decay measurements yielded insight into the modulation of rotational dynamical behavior of the drug within the bile salt aggregates. © 2017 Elsevier Inc.

Journal of Colloid and Interface Science

Differential interaction behaviors of an alkaloid drug berberine with various bile salts

In this article, the binding interactions of a promising chloride channel blocker 9-methyl anthroate (9-MA) with a series of bile-salt aggregates of varying hydrophobicity have been thoroughly demonstrated. The altered photophysical properties of the fluorescent probe within the concerned microheterogeneous environments have been exploited spectroscopically to assess the communication between the aggregates and the guest. The contrived hydrophobic environment provided by the aggregates appreciably diminishes the water-assisted non-radiative decay channels and thus extends the fluorescence lifetime and the rotational relaxation time of the probe. NaDC aggregates, being more rigid and hydrophobic, provide a better protection to the bound guest from the external influence which is apparent from a much longer fluorescence lifetime and rotational correlation time for the encapsulated probe in NaDC aggregates compared to those in NaC and NaTC aggregates, as is further validated by fluorescence quenching experiments. Salt induced alterations of the binding behavior of the probe with the bile-salt aggregates have also been evaluated via fluorimetric studies, which conclude larger and tighter aggregate formation resulting in a superior degree of rigidity imposed on the aggregate-bound probe at high ionic strength of the medium. © The Royal Society of Chemistry and Owner Societies 2015.

Photochemical and Photobiological Sciences

Modulated photophysics of an anthracene-based fluorophore within bile-salt aggregates: The effect of the ionic strength of the medium on the aggregation behavior

The present work demonstrates the photophysical characterization of the interaction of a promising cancer cell photosensitizer, harmane (HM), with biomimetic micellar nanocavities having varying surface charge characteristics. The polarity-sensitive prototropic transformation of HM is remarkably modified upon interaction with the macromolecular assemblies of micellar systems and is manifested through significant modulations on the absorption and emission profiles of HM. The ground- and excited-states prototropic equilibria of HM are found to be differentially modulated in various micellar assemblies. Out of various possibilities to assess the drug (HM)-micelle interaction mechanism, the postulate of varying extent of drug penetration into micellar units depending on the compactness of their headgroup arrangements is found to suitably rationalize and correlate different experimental findings, including the differences in binding constant (K) and free energy change (δG) of the interaction process. The micropolarity measurement has been exploited to evaluate the probable binding location of the drug which reveals that the cationic drug molecule does not penetrate deep into the micellar core region and the results are further substantiated from fluorescence quenching experiments. The work also pays proper attention to delineate the modulation in dynamical behaviors of the drug following interaction with the micellar systems. Wavelength-sensitive fluorescence parameters reveal the slower rate of solvent-relaxation around the excited probe within the micelle-encapsulated microheterogeneous environments. The enhancement of fluorescence anisotropy and rotational relaxation time of the drug in micellar environments from that in pure aqueous buffer suggests entrapment of the drug in motionally constrained regions introduced by the micelles. © 2012 American Chemical Society.

Journal of Physical Chemistry B

Binding interaction and rotational-relaxation dynamics of a cancer cell photosensitizer with various micellar assemblies

The present work describes the interaction of a promising cancer cell photosensitizer, harmane (HM), with a model transport protein, Bovine Serum Albumin (BSA). The studied molecule of interest (HM) belongs to the family of naturally occurring fluorescent drug-binding alkaloids, the β-carbolines. A combined use of steady-state and time-resolved fluorescence techniques is applied to follow and characterize the binding interaction. The polarity-dependent prototropic activity of HM is found to be responsible for the commendable sensitivity of the probe to the protein environments and is distinctly reflected on the emission profile. Steady-state fluorescence anisotropy study reveals the impartation of a considerable degree of motional restriction on the drug molecule as a result of binding to the protein. Contrary to the single-exponential nature of fluorescence anisotropy decay of HM in aqueous buffer, they are found to be biexponential in the protein environment. The rotational relaxation dynamics of HM within the protein has been interpreted on the lexicon of the Two-Step and Wobbling-in-Cone model. The probable binding location for the cationic drug is found to be the hydrophilic binding zone of BSA, i.e., domain I (characterized by a net negative charge). The AutoDock-based blind docking simulation has been explored for evaluating an unbiased result of the probable interaction site of HM in the protein. To unfold the effect of binding of the drug on the secondary structural content of the protein, circular dichroism (CD) spectroscopy has been exploited to see that binding of the drug accompanies some decrease in α-helical content of BSA, and the effect gradually saturates toward a higher drug/protein molar ratio. © 2011 American Chemical Society.

Modulation of prototropic activity and rotational relaxation dynamics of a cationic biological photosensitizer within the motionally constrained bio-environment of a protein

A simple intramolecular charge transfer (ICT) compound, 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester (DPDAME), has been documented to be a potential molecular reporter for probing microheterogeneous environments of a model transport protein bovine serum albumin (BSA) using spectroscopic techniques. Meteoric modifications to the emission profile of DPDAME upon addition of BSA come out to be a result of its binding to hydrophobic subdomain IIA. The highly polarity-sensitive ICT emission of DPDAME is found to be a proficient extrinsic molecular reporter for efficient mapping of native, intermediate, unfolded, and refolded states of the protein. Experimental data coupled with a reinforcing support from theoretical simulation using CHARMM22 software confirm the binding site of the probe to be the subdomain IIA of BSA, while FRET study reveals a remarkably close approach of our extrinsic molecular reporter to Trp-212 (in domain IIA): the distance between DPDAME and Trp-212 is 1.437 nm. The caliber of DPDAME as an external fluorescence marker also extends to the depiction of protein-surfactant (BSA-SDS) interaction to commendable fruition. Additionally, the protective action of small amounts of SDS on urea-denatured protein is documented by polarity-sensitive ICT emission of the probe. The present study also reflects the enhancement of the stability of BSA with respect to chemically induced denaturation by urea as a result of binding to the probe DPDAME. © 2010 American Chemical Society.

Exploring hydrophobic subdomain iia of the protein bovine serum albumin in the native, intermediate, unfolded, and refolded states by a small fluorescence molecular reporter

Differential Perturbation of the Protrotropic Equilibrium of a Biological Photosensitizer within Bile Salt Aggregates of Varying Hydrophobicity: A Fluorimetric Investigation

Journal	Photochemistry and Photobiology
Publisher	Blackwell Publishing Inc.
ISSN	0031-8655
Open Access	No